The present invention relates to exhaust system and pollution control devices, such as catalytic converters, diesel particulate filters or traps, exhaust pipes and the like. In particular, the invention relates to an internal insulating liner used in high temperature applications. The application describes the invention as it relates to an internally insulating end cone used to provide a transition from an exhaust pipe to the pollution control device. The end cone comprises a metal inlet or outlet cone housing with a free-standing fiber-based composite cone positioned within the metal cone housing. The internal fiber based cone does not require a protective metal internal cone housing.
Pollution control devices such as catalytic converters and diesel particulate filters or traps are well known, and are most typically used to purify the exhaust gasses produced by internal combustion engines. These types of pollution control devices typically comprise a metal housing with a monolithic element securely mounted within the casing by a resilient and flexible mounting mat.
Two types of devices are currently in wide spread usexe2x80x94catalytic converters and diesel particulate filters or traps. Catalytic converters contain a catalyst, which is typically coated on a monolithic structure mounted in the converter. Monolithic structures are typically ceramic, although metal monoliths have been used. The catalyst oxidizes carbon monoxide and hydrocarbons, and reduces the oxides of nitrogen in automobile exhaust gases to control atmospheric pollution. Diesel particulate filters or traps are wall-flow filters which have honeycombed monolithic structures typically made from porous crystalline ceramic materials. Alternate cells of the honeycombed structure are typically plugged such that exhaust gas enters one cell and is forced through the porous wall of one cell and exits the structure through another cell.
Due to the relatively high temperatures encountered in pollution control devices, it is important that the device be well insulated. Insulation is typically provided by securely mounting the monolithic element within the casing using an insulating mounting mat comprised of a suitable material. In addition, inlet and outlet cones which provide a transition from the exhaust pipe to the pollution control device are also insulated. The inlet and outlet end cones have previously been insulated by providing a double-walled end cone comprising an outer metal housing and an inner metal housing, with a gap defined between the inner and outer cone housings. A suitable insulating material fills the gap between the inner and outer cone housings. Examples of dual-wall end cones can be seen, for example, in U.S. Pat. No. 5,408,828 to Kreucher et al. Kreucher et al. shows the catalytic converter having a two-walled defuser leading from an exhaust pipe to the catalytic converter. A thermal insulating air barrier is provided between the inner wall and outer wall. Another example of double-walled end cones is seen in German Patent No. 3,700,070 A1 which shows an insulating mat placed between an outer and inner end cone.
The use of double-walled end cones has been required due to the nature of the insulating material used in pollution control devices. In particular, the use of low-density fibrous insulating materials requires an inner cone, because exposure to exhaust gases causes rapid erosion and destruction of the low-density fibrous insulating material. In addition, as it erodes the fibrous insulating material tends to clog the monolithic structure of the pollution control device and degrade its performance. Thus, the protective inner end cone was required to maintain the position and structural integrity of the insulating material. This is also true with other insulating materials which have been used as ceramic beads, such as shown in U.S. Pat. No. 5,419,127 to Moore, III. Moore shows an insulated exhaust manifold having a layer of insulating ceramic beads between an inner and outer exhaust manifold.
Although required for maintaining the position and structural integrity of the insulating layer of the inlet and outlet cones, the use of a protective metal inner cone has several disadvantages. In particular, use of an inner metal cone significantly increases the weight of the device, as well as the cost to manufacture the device. Therefore, what is needed is an insulating end cone which does not require use of a protective inner cone, and insulating material which is resistant to damage caused by exposure to hot exhaust gases and road shock.
The present invention provides a self-supporting insulating liner for use with exhaust systems and pollution control devices. The application describes the invention as it relates to an insulating end cone for use with pollution control devices such as catalytic converters and diesel particulate filters or traps. The end cone comprises an outer metallic end cone for connection to an exhaust system and a pollution control device. Within the outer end cone is an insulating cone positioned such that a substantial portion of the inner surface of the insulating cone is exposed to hot exhaust gases from the internal combustion engine, and the outer surface of the insulating cone is positioned adjacent the outer metallic end cone. The self supporting insulating liner thus eliminates the need for an inner metallic liner to protect the insulation. In a preferred embodiment, the insulating liner is formed of a composite material which utilizes glass or ceramic fibers mixed with a binder to create a rigid, yet shock resistant insulating end cone.